Controlling powertrain components for hill-holding in a hybrid electric vehicle

ABSTRACT

A hybrid electric vehicle includes an engine and a traction motor coupled to the engine by a coupling device or a clutch for providing torque to wheels of the vehicle. An inverter is electrically connected to the traction motor. A second coupling device or at least one clutch at least indirectly selectively couples the motor to the drive wheels. A controller controls the second coupling device based upon a temperature of at least one of the fraction motor and the inverter.

TECHNICAL FIELD

The present disclosure is directed to a hill-hold in a hybrid electricvehicle.

BACKGROUND

Hybrid electric vehicles (HEV's) include an internal combustion engineand an electric traction motor, both being capable of propelling theHEV. When the operator of the HEV desires that the vehicle remainmotionless, the vehicle can be at rest with the engine either on or off.When the vehicle is at rest with the engine on, a clutch downstream ofthe engine can be slipped in order to keep the engine from stalling.When the vehicle is at rest with the engine off, the motor can continueto spin with the downstream clutch open, or the motor can be disabled.

While the HEV is on an incline, the engine and/or motor must work toprovide power to the wheels if the operator of the HEV desires that thevehicle remain motionless. This is known as hill-hold. There exists aneed for a hill-hold system that holds the HEV on an incline by moreefficiently utilizing the engine and/or the traction motor to providetorque to the wheels.

SUMMARY

According to one embodiment of the present disclosure, a vehiclecomprises an engine and a traction motor for providing torque to atleast one drive wheel. A first coupling device, or a clutch, selectivelycouples the engine to the traction motor. An inverter is electricallyconnected to the traction motor. A second coupling device is providedthat, at least indirectly, couples the traction motor to the wheels. Oneor more controllers are provided that communicate with variouscomponents in the vehicle. The one or more controllers are configured tocontrol the second coupling device. The second coupling device iscontrolled based at least upon a temperature of at least one of thetraction motor and the inverter. In one embodiment, the controller isconfigured to at least partially disengage the second coupling devicebased upon the temperature of at least one of the traction motor and theinverter exceeding a first threshold. The engine may be activated basedupon the temperature exceeding the first threshold, the activation beinggenerally simultaneous with the disengagement of the second couplingdevice.

According to another embodiment of the present disclosure, a hill-holdsystem for a vehicle is provided. The system comprises an engine and amotor for providing torque to at least one drive wheel. An inverter iselectrically connected to the motor. A clutch, at least indirectly,selectively couples the motor to the wheels. A controller is alsoprovided that activates a first drive mode and a second drive mode. Inthe first drive mode, the clutch is locked and the engine is disabled.In the second drive mode, the clutch is partially disengaged and theengine is activated. The controller is configured to activate the seconddrive mode based upon a temperature of at least one of the motor and theinverter exceeding a threshold.

According to yet another embodiment of the present disclosure, a methodfor controlling hill-hold of a vehicle is provided. A temperature of atleast one of a traction motor and an inverter is determined. A clutch isunlocked based upon the determined temperature being above a threshold.The clutch is disposed between the traction motor and traction wheels.An engine is activated to power the wheels generally simultaneously withthe unlocking of the clutch. The torque of the traction motor may alsobe reduced generally simultaneously with the activation of the engine.Once the temperature of the traction motor and the inverter increaseabove a second threshold, the clutch may be locked and the torque in themotor may be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a hybrid electric vehicleaccording one embodiment of the present disclosure;

FIG. 2 is a schematic illustration of a transmission and other drivelinecomponents of a hybrid electric vehicle according to one embodiment ofthe present disclosure;

FIG. 3 is a graph illustrating an example of vehicle speed andtransmission input speed over time when a clutch is locked;

FIG. 4 is a graph illustrating an example of vehicle speed andtransmission input speed over time while a clutch transitions betweenslipping and not slipping;

FIG. 5 is a graph illustrating inverter temperature and motortemperature during times in which at least one of the motor and engineare holding the vehicle on a hill according to one embodiment of thepresent disclosure;

FIG. 6 is a flowchart illustrating a method according to one embodimentof the present disclosure; and

FIG. 7 is a flowchart illustrating another method according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the present invention are disclosed herein. Itis to be understood that the disclosed embodiments are merely exemplaryof the invention that may be embodied in various and alternative forms.The figures are not necessarily to scale, as some features may beexaggerated or minimized to show details of particular components.Specific structural and functional details disclosed herein aretherefore not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIG. 1, a schematic diagram of a vehicle 10 is illustratedaccording to one embodiment of the present disclosure. The vehicle 10 isan HEV. The powertrain of the HEV includes an engine 12, an electricmachine or motor/generator (M/G) 14, and a transmission 16 disposedbetween the M/G 14 and wheels 18. A torque converter 19 can optionallybe provided between the M/G 14 and the transmission 16. The torqueconverter 19 transfers rotating power from the M/G 14 to thetransmission 16. It should be understood that instead of a torqueconverter 19, one or more clutches can be provided to selectivelytransfer torque from the M/G 14 to the transmission 16.

The M/G 14 can operate as a generator in one fashion by receiving torquefrom the engine 12 and supplying AC voltage to an inverter 20, wherebythe inverter 20 converts the voltage into DC voltage to charge atraction battery, or battery 22. The M/G 14 can operate as a generatorin another fashion by utilizing regenerative braking to convert thebraking energy of the vehicle 10 into electric energy to be stored inthe battery 22. Alternatively, the M/G 14 can operate as a motor, inwhich the M/G 14 receives power from the inverter 20 and battery 22 andprovides torque as an input to the torque converter 19 (or clutch),through the transmission 16 and ultimately to the wheels 18. Adifferential 24 can be provided to distribute torque from the output ofthe transmission 16 to the wheels 18.

A first coupling device, or disconnect clutch 26 is located between theengine 12 and the M/G 14. The disconnect clutch 26 can be fully open,partially engaged, or fully engaged (locked). In order to start theengine 12, the M/G 14 rotates the engine 12 when the disconnect clutch26 is at least partially engaged. Once the engine 12 is rotated by theM/G 14 to a certain speed (e.g., ˜100-200 rpm), fuel entry and ignitioncan commence. This enables the engine 12 to “start” and to providetorque back to the M/G 14, whereby the M/G 14 can charge the battery 22and/or power the wheels 18 to propel the vehicle 10. Alternatively, aseparate engine starter motor (not shown) can be provided.

The vehicle 10 also includes a control system, shown in the embodimentof FIG. 1 as three separate controllers: an engine control module (ECM)28, a transmission control module (TCM) 30, and a vehicle systemcontroller (VSC) 32. The ECM 28 is directly connected to the engine 12,and the TCM 30 can be connected to the M/G 14 and the transmission 16.The three controllers 28, 30, 32 are connected to each other via acontroller area network (CAN) 34. The VSC 32 commands the ECM 28 tocontrol the engine 12 and the TCM 30 to control the M/G 14 and thetransmission 16. Although the control system of the vehicle 10 includesthree separate controllers, such a control system can include more orless than three controllers, as desired. For example, a separate motorcontrol module can be directly connected to the M/G 14 and to the othercontrollers in the CAN 34.

As illustrated in FIG. 1, τ_(eng) and ω_(eng) refer to the torque andspeed of the engine, respectively. Furthermore, τ_(mot) and ω_(mot)refer to the torque and speed of both sides of the motor 14,respectively. τ_(in) and ω_(in) refer to the torque and speed of theinput of the transmission 16, downstream of the torque converter 19,respectively, while τ_(out) and ω_(out) refer to the torque and speed ofthe output of the transmission 16. The final torque and speedtransmitted to the wheels 18 is represented by τ_(final) and ω_(final),downstream of the engagement with the differential 24.

Referring to FIG. 2, the transmission 16 is shown in detail. It shouldbe understood that FIG. 2 merely exemplifies one configuration of atransmission 16. In a vehicle 10 utilizing the exemplified configurationof FIG. 2, a torque converter may not be needed in the vehicle, due tothe multiple clutches and planetary gearsets within the transmission. Itshould therefore be understood that a simplified transmission 16 can beutilized in combination with a torque converter, in which fewer clutchesand planetary gearsets are needed within the transmission 16. Severalother embodiments are contemplated with various configurations ofclutches and/or planetary gearsets, with or without the use of a torqueconverter, as known in the art.

The transmission 16 of FIG. 2 includes an input shaft 40 that receivestorque from the engine 12 and the M/G 14 either separately or incombination. The input shaft 40 is operatively connected to a secondclutch 42 and a third clutch 44. A portion of each of the second clutch42 and third clutch 44 is connected to a first planetary gearset (PG)46, which is connected to a second planetary gearset (PG) 48. A reverseclutch, or fourth clutch 49 and a low-and-reverse brake, or fifth clutch50 can also be connected to the PG 48. The second PG 48 drives a belt orchain 52 to transmit power to a third planetary gearset (PG) 54. Each ofthe planetary gearsets 46, 48, 54 can include a sun gear, a ring gear,and a planetary carrier to provide various gear ratios in thetransmission 16. The third PG 52 provides a final gear ratio to transmittorque from the transmission 16 to the differential 24.

A pump 56 provides pressure to each of the clutches to engage/disengageeach clutch as dictated by the TCM 30. It should be understood that oneor more of the clutches 42, 44, 49, 50 can be controlled to be engaged(locked), partially engaged, or fully disengaged, similar to theoperation of the disconnect clutch 26. For example, when the secondclutch 42 and/or the third clutch 44 are disengaged, the transmission 16can be isolated from the M/G 14 such that no torque is transmittedthrough the transmission 16 and to the wheels 18. It should also beunderstood that while clutches 42, 44 are illustrated as being a part ofthe transmission 16, one or more clutches can be separately utilizedbetween the M/G 14 and the transmission 16 instead of being integralwith the transmission 16.

Referring to FIGS. 1-2, the engine 12 and M/G 14 can individually ortogether work to provide a relatively small amount of power to thewheels 18 to maintain the vehicle 10 motionless on an incline. This ishereinafter referred to as a hill-hold. When an operator of the vehicle10 is stopped or idled on an incline, a release of the brake pedalshould not enable the vehicle 10 to begin rolling backwards. The engine12 and/or M/G 14 can provide torque to the wheels 18 to either maintainthe vehicle 10 in a motionless state, or, if the incline is relativelysmall, provide a small amount of forward motion or “creeping” to thevehicle 10.

During hill-hold, if the M/G 14 is providing the necessary torque to thewheels 18 without the engine 12 activated, a coupling device or clutchdownstream of the M/G 14 can be locked such that the torque istransferred through the transmission 16 and to the wheels 18. At aparticular moment, as will be discussed further, the clutch can beunlocked such that the engine 12 can be activated by the M/G 14 andbegin to provide torque to the wheels and continue the hill-hold. Thepresent disclosure provides a system that determines whether to use theengine 12 or M/G 14, and when to lock or unlock the clutch in order toprovide hill-hold functionality. While references in the presentdisclosure are made to a “clutch” or a “coupling device” that is lockedor unlocked during hill-hold, it should be understood that the “clutch”or “coupling device” can refer to one or more clutches downstream of theM/G 14 that, at least indirectly, couple the M/G 14 to the wheels 18such that torque from the M/G 14 is translated into power at the wheels18. For example, the clutch can be any clutch in the transmission 16,such as clutches 42 and 44. The clutch can also be a bypass clutch inthe torque converter 19, or a clutch disposed between the M/G 14 andtransmission 16 if a torque converter 19 is not included in the vehicle10. Furthermore, the clutch can also refer to the combination of thetorque converter 19 and the transmission 16. In all referenceshereinafter in the present disclosure to a “clutch”, it should beunderstood that any of the above-referenced clutches or combinations ofclutches are contemplated unless otherwise indicated.

Referring to FIG. 3, a graph is provided that illustrates an example ofan electric mode of operation in which the M/G 14 propels the vehicle 10and the engine 12 is disabled. As shown in FIG. 3, the input speed(ω_(in)) of the transmission 16 and the speed of the vehicle 10 resembleone another. This is due to the clutch being locked and not slipping.Before time T1 and after time T2, the vehicle has a speed of 0 mph. Thisindicates that the vehicle is either stopped or idling, and either on aflat surface or on an incline. It is during these times that the engine12, M/G 14 and clutch downstream of the M/G 14 must be controlled if thetorque of the engine 12 is needed to maintain the hill-hold.

Referring to FIG. 4, an alternate embodiment is provided thatillustrates an example in which the clutch alternates between slippingand not slipping during vehicle travel. In this case, the M/G 14 isallowed to spin at a predetermined speed or “idle speed” when thevehicle 10 is at rest. Before T1, the vehicle 10 is motionless, the M/G14 is spinning, the clutch is slipping. It should be noted that in thisillustrated embodiment, since the speed of the input of the transmission16 (ω_(n)) is positive, the clutch that is slipping is a clutchdownstream of the torque converter 19. The clutch can thus be clutch 42,44 in the transmission, for example.

At point T1, the input speed of the transmission 16 increases as thevehicle beings to be propelled. The pressure in the clutch can increase,but the clutch is still slipping between times T1 and T2. The vehicle 10can be creeping, for example, between times T1 and T2. At time T2, theclutch is locked and the input speed of the transmission 16 resemblesthe speed of the vehicle 10. Between times T2 and T3, the vehicle 10travels with no clutch slip such that the changes in the M/G 14correspond to changes in the input speed of the transmission 16 which,in turn, corresponds to changes in the vehicle speed. At time T3, theclutch unlocks and beings to slip, while the speed of the M/G 14 returnsto idle speed and the input speed of the transmission 16 continues todecrease as the vehicle 10 slows to a stop. At time T4, the vehicle 10is again stopped with the M/G 14 spinning and the clutch slipping.

As previously disclosed, the vehicle 10 must remain motionless withminimal disturbances for a satisfactory hill-hold. Therefore, duringhill-hold, a control system must be provided when the engine 12 isneeded to be activated or the torque at least increased, as previouslydescribed. An example of such a system will now be described withreference to FIGS. 5-7.

Referring to FIG. 5, the temperature of the M/G 14 (“motor temp”) aswell as the temperature of the inverter 20 (“inverter temp”) areillustrated during a hill-hold cycle. For each of the inverter temp andthe motor temp, a hysteresis line is also provided. The “inverter temphysteresis” and the “motor temp hysteresis” represent time-delayed dataas a function of the inverter temp and motor temp data, respectively.

Before time T1, hill-hold is accomplished with the M/G 14 and the engine12 deactivated with the clutch locked. The temperature of the inverter20 and the M/G 14 continues to increase as hill-hold is accomplished bythe M/G 14 due to the flow of electric power from the battery 22 to theM/G 14.

At time T1, the temperature of the inverter 20 has increased above apredetermined calibrated inverter temperature (“Inverter Temp Cal”).This calibrated temperature is preferably greater than 200° F., but canbe any calibrated to any temperature in which a threat of heat damagecan be present. At T1, the clutch is slipped to off-load the heat fromthe M/G 14. In order to supplement the power demands at the wheels 18for hill-hold purposes while the clutch is slipped, the engine 12 isactivated at T1. The activation of the engine 12 and the slipping of theclutch occurs generally simultaneously, preferably within a fraction ofa second. Once the engine 12 is activated, the clutch is opened orslipped such that the speed transmitted is no lower than the engine's 12idle speed to prevent the engine 12 from stalling.

Between times T1 and T2, the engine 12 continues to provide thenecessary torque through the powertrain to maintain the vehicle 10 in ahill-hold. As the engine 12 remains activated, the M/G 14 and theinverter 20 cool down due to their inactivity. The engine 12 is able toprovide torque to the wheels 18 for a hill-hold. The engine 12 can alsoprovide the necessary power to charge the battery 22 if needed, in themanner as previously disclosed.

At time T2, the inverter temp hysteresis has decreased below thepredetermined calibrated inverter temperature amount, and the motor temphysteresis has decreased below the predetermined calibrated motortemperature amount. It should be understood that the calibrated invertertemperature value and the calibrated motor temperature value can bedifferent when the engine 12 is on as opposed to the engine 12 beingoff. In other words, the calibrated temperature values for the inverterand motor can be lower or higher when the inverter 20 and M/G 14 arecooling than when the inverter 20 and M/G are heating.

When both of the inverter and motor temp hysteresis values havedecreased below the calibrated values at time T2, the temperatures ofthe inverter 20 and M/G 14 are determined to be at a safe temperaturesuch that the clutch can lock and the M/G 14 can again work to providethe necessary torque for a hill-hold. After time T2, the inverter tempand the motor temp rise again, due to the work provided to hold thevehicle 10 on an incline.

Referring to FIG. 6, one example of a method of a hill-hold is providedin which the clutch can be locked and the M/G 14 is at 0 mph while thevehicle 10 is at rest. The VSC 32 and other controllers implement theillustrated example. The method begins at step 100. At step 102, adetermination is made as to whether the clutch is locked. If the clutchis locked, a determination is made as to whether the temperature of theM/G 14 is above the predetermined calibrated motor temperature at step104. If not, then a determination is made as to whether the temperatureof the inverter 20 is above the predetermined calibrated invertertemperature at step 106. If either temperature is above respectivepredetermined values, the clutch is unlocked at step 108. At step 110,which can be generally simultaneous with step 108, a request is made topull-up and activate the engine 12, and the torque of the M/G 14 isreduced. This allows the M/G 14 and the inverter 20 to cool while notproviding torque to the wheels 18.

If the clutch is locked as determined at step 102, then at step 112 adetermination is made as to whether the temperature of the M/G 14 isless than the calibrated motor temperature hysteresis. If so, then adetermination is made as to whether the temperature of the inverter 20is less than the calibrated inverter temperature hysteresis at step 114.If a positive determination is made at steps 112 and 114, thetemperature of both the M/G 14 and the inverter 20 has reached a safelimit such that the M/G 14 can be increased in torque to providehill-hold. At step 116, the clutch is locked. At step 118, which can besimultaneous with step 116, a request is made to disable the engine, andthe torque of the M/G 14 is increased to provide hill-hold. The methodends at 120, at which time the method can repeat again at step 100.

Referring to FIG. 7, another example of an algorithm for a hill-hold isprovided, in which the M/G 14 remains spinning while the vehicle 10 isat rest. The VSC 32 and other controllers implement the illustratedexample. The method begins at step 200. At step 202, a determination ismade as to whether the engine 12 is activated. If the engine 12 is notactivated, then at step 204 a determination is made as to whether thetemperature of the M/G 14 is above the predetermined calibrated motortemperature value. If the M/G 14 is not too hot, a determination is madeat step 206 as to whether the inverter 20 is too hot (i.e., thetemperature of the inverter 20 is above the predetermined calibratedinverter temperature. If a positive determination is made at eithersteps 204 or 206, then at step 208 a request is made to activate theengine 12 as well as reduce the torque of the M/G 14. The engine 12 thusaccomplishes the hill-hold while the M/G 14 and inverter are cooled.

If the engine was determined to be activated at step 202, then at step210 a determination is made as to whether the temperature of the M/G 14is less than the calibrated motor temperature hysteresis. If so, then afurther determination is made as to whether the temperature of theinverter 20 is less than the calibrated inverter temperature hysteresisat step 212. If a positive determination is made at steps 210 and 212,the temperature of both the M/G 14 and the inverter 20 has reached asafe limit such that the M/G 14 can be increased in torque to providehill-hold. Thus, the engine is disabled at step 214 at the torque of theM/G 14 is increased to provide the necessary torque to the wheels 18.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation. It is also contemplated that various embodiments of thepresent disclosure may be combined or rearranged to achieve a specificresult. Furthermore, to the extent that particular embodiments describedherein are described as less desirable than other embodiments or priorart implementations with respect to one or more characteristics, theother embodiments and the prior art implementations are not outside thescope of the disclosure and may be desirable for particularapplications.

What is claimed is:
 1. A vehicle comprising: an engine; a tractionmotor; a first coupling device for selectively coupling the engine tothe traction motor; an inverter electrically connected to the tractionmotor; a second coupling device for selectively coupling the tractionmotor to the wheels; and a controller configured to at least partiallydisengage the second coupling device and activate the engine based upona temperature of at least one of the traction motor and the inverter. 2.The vehicle of claim 1, wherein the controller is configured to at leastpartially disengage the second coupling device in response to thetemperature of at least one of the traction motor and the inverterexceeding a first threshold.
 3. The vehicle of claim 2, wherein thecontroller is further configured to lock the first coupling device andactivate the engine in response to the temperature exceeding the firstthreshold.
 4. The vehicle of claim 3, wherein the controller is furtherconfigured to lock the second coupling device in response to thetemperature of both of the traction motor and the inverter being below asecond threshold.
 5. The vehicle of claim 4, wherein the controller isfurther configured to deactivate the engine in response to thetemperature of both of the traction motor and the inverter being belowthe second threshold.
 6. The vehicle of claim 1, wherein the controlleris further configured to control the first coupling device in responseto the temperature of at least one of the traction motor and theinverter.
 7. The vehicle of claim 1, wherein the second coupling deviceis a torque converter disposed between the traction motor and thewheels.
 8. The vehicle of claim 1, wherein the second coupling device isa clutch disposed between the traction motor and the wheels.
 9. Ahill-hold system for a vehicle comprising: an engine; a motor forproviding torque to wheels; an inverter electrically connected to themotor; a clutch for selectively coupling the motor to the wheels; and acontroller configured to: activate a first drive mode in which theclutch is locked and the engine is off, activate a second drive modebased upon a temperature of at least one of the motor and the inverterexceeding a threshold, wherein in the second drive mode the clutch ispartially disengaged and the engine is on, and subsequent to activatingthe second drive mode, activate the first drive mode based upon thetemperatures of the motor and the inverter reducing below the threshold.10. The system of claim 9, further comprising a second clutch disposedbetween the engine and the motor for selectively coupling the engine tothe motor.
 11. The system of claim 9, wherein the controller is furtherconfigured to activate the first drive mode based upon the temperatureof both of the inverter and the motor being below a second threshold.12. The system of claim 9, wherein the clutch is disposed within atransmission such that the motor selectively provides torque through thetransmission and to the wheels.
 13. A vehicle comprising: an engine; atraction motor for providing torque to wheels; a first coupling devicefor selectively coupling the engine to the traction motor; an inverterelectrically connected to the traction motor; a second coupling devicefor selectively coupling the traction motor to the wheels; and acontroller programmed to control the first and second coupling devicesbased upon a temperature of at least one of the traction motor and theinverter.